1. Field
The disclosure relates to a method and apparatus for a heterojunction barrier diode (“HBD”). More specifically, the disclosure relates to a highly sensitive diode detector having a heterojunction barrier layer providing detection sensitivity of about 20,000 V/W or more while having low capacitance.
2. Description of the Related Art
A focal-plane array (“FPA”) is an image sensing device consisting of an array (typically rectangular) of light-sensing pixels at the focal plane of a lens. Conventional FPAs are used for imaging purposes such as photography or videography. More advanced FPAs are used for non-visual imaging purposes such as spectroscopy, light detection, and wave-front sensing. While FPAs cover a variety of imaging devices, its most common usage is for two-dimensional imaging devices that are sensitive in the infrared (“IR”) spectrum. Devices which are sensitive in other spectra are conventionally referred to by other terms, such as Charge-Coupled Device (“CCD”) and CMOS image sensor in the visible spectrum.
FPAs operate by detecting photons and generating an electrical charge, voltage or resistance in proportion to the number of photons detected. The charge relates to the photons received at each pixel. The charge, voltage or resistance is then measured, digitized, and used to construct an image of the object, scene, or the phenomenon that emitted the photons.
In the millimeter wave and terahertz regions, FPA detectors are complex and expensive. This is largely due to the sensitivity required for extracting the minimal passive radiation which is available in the millimeter wave and terahertz regions. Passive radiation is not available in IR and hence is not a factor in the FPA design. Such complexity renders the FPAs operating in the terahertz range expensive, complex and fragile. A direct detector substantially reduces the required complexity. However, the direct detectors do not have the sensitivity required for imaging applications. Therefore, there is a need for a detector having ultrahigh sensitivity.